Rotary joint

ABSTRACT

A mechanical seal rotary joint of the end-face contact type which permits slurry fluids, such as polishing solution, to pass through a fluid passage without leaking out of the relatively rotating contact area therein. The rotary joint of the present invention comprises: a first joint body ( 1 ); a second joint body ( 2 ) connected rotatably to the first joint body ( 1 ); a prime seal unit ( 3 ) provided between the opposed end portions ( 11, 21 ) of the two joint bodies ( 1, 2 ); and a continuous line of prime fluid passage ( 6 ). The prime seal unit ( 3 ) is a mechanical seal comprising: a stationary seal ring ( 30 ) fixed on the end portion ( 21 ) of the second joint body ( 2 ) concentrically with the axis of rotation as its center; a movable seal ring ( 31 ) held on the end portion ( 11 ) of the first joint body ( 1 ) and concentric with and opposite to the stationary seal ring ( 30 ); a rotation stopper ( 32   a ) provided on the outer circumferential side of the movable seal ring ( 31 ) for preventing the relative rotation of the seal ring ( 31 ) while allowing the seal ring ( 31 ) to move in the axial direction; and springs ( 33   a ) to thrust and press the movable seal ring ( 31 ) against the stationary seal ring ( 30 ). Thus, the prime seal unit ( 3 ) is constructed so as to provide a seal between the inner circumferential region ( 3   a ) and the outer circumferential region ( 3   b ) of the two seal rings ( 30, 31 ). The prime fluid passage ( 6 ) is made up of the inner circumferential regions ( 3   a ) of the two seal ring ( 30, 31 ), a first primary passage section ( 60 ) passing through the first joint body ( 1 ) and leading into the inner circumferential region ( 3   a ) and a second prime fluid passage section ( 61 ) passing through the second joint body ( 2 ) and leading into the inner circumferential region ( 3   a ). A slurry fluid ( 106 ), such as a polishing solution, flows through the prime fluid passage ( 6 ) without leaking out of the relatively rotating section of the joint bodies ( 1, 2 ).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to rotary joints for fluids, and morespecifically to rotary joints that allow fluids—such as polishingsolution for polishing the surface of silicon wafer by the chemicalmechanical polishing (CMP) technique—to flow through the components thatrotate relative to one another.

2. Description of the Prior Art

An apparatus for polishing the surface of silicon wafers by CMP, towhich this invention relates, has been developed in recent years. Theapparatus, as shown in FIGS. 10 and 11, comprises: a rotary table 102that rotates horizontally; a pad shaft support block 103 which moveshorizontally back and forward and up and down; a polishing pad shaft 104which, held by the pad shaft support block 103, is forced to rotate; aslurry fluid feeding and discharging passage 105 formed on thenon-rotary side in the pad shaft support block 103; a feeding anddischarging mechanism 107 connected to the slurry fluid feeding anddischarging passage 105 for a polishing solution 106, for example, aKOH-contained silica slurry mixed in isopropyl alcohol; a slurry fluidfeeding and discharging passage 108 on the rotary side which runsthrough the polishing pad shaft 104 and opens at the central portion ofa pad head 104 a; and a rotary joint 101 which, installed between thepad shaft support block 103 and the polishing pad shaft 104, connectsthe two slurry fluid feeding and discharging passages 105 and 108 insuch a way that the two passages 105 and 108 are relatively rotatablewhen communicating with each other.

By that surface polishing apparatus, the silicon wafer 109 is polishedin this way: first, the silicon wafer 109 is held on the rotary table102, the surface 109 a up, and the polishing pad shaft 104 is moved downuntil the pad head 104 a comes into contact with the wafer surface 109a. Then, the polishing solution 106 is jetted out to between the padhead 104 a and the wafer 109 by means of positive pressure action(jetting operation of the polishing solution pump) of the feeding anddischarging mechanism 107. And the polishing pad shaft 104 is rotatedand moved back and forward horizontally to polish the wafer surface 109a. After polishing is over, the feeding and discharging mechanism 107 isswitched to negative pressure action (sucking operation of the polishingsolution pump) to suck and remove the residues of the polishing solution106 in the slurry fluid feeding and discharging passages 105 and 108.That is, care is taken so that the residues of the polishing solution106 in the slurry fluid feeding and discharging passages 105 and 108 maynot drop on the polished surface of the wafer, and that is effected byswitching the slurry fluid feeding and discharging passages 105, 108from the positive pressure mode to the negative pressure or dry mode.

The rotary joint 101 mounted in that surface polishing apparatus isdesigned as in the following. A first joint body, which is to be mountedon the pad shaft support block 103, is connected to a second joint body,which is to be fixed on the polishing pad shaft 104 such that the firsjoint body and the second joint body may rotate relative to one another.Within the first joint body is formed a first fluid passage sectionwhich is connected to the slurry fluid feeding and discharging passage105 on the non-rotary side. In the second joint body on the rotary sideis formed a second fluid passage section that is connected to the slurryfluid feeding and discharging passage 108. A space formed between thetwo slurry fluid passage sections is sealed with a sealing member placedbetween the relatively rotating opposed faces of the first joint bodyand the second joint body. An example of such a sealing member issealing faces formed on the opposing parts of the relatively rotatingfirst and second joint bodies that are brought into contact with andpressed against each other. Another example to seal the relativelyrotating parts is elastic seal materials such as O-ring.

The rotary joint 101 of such a design presents the following problems.That is, the polishing solution 106 is a slurry fluid containingabrasive grains. Those abrasive grains tend to intrude and be depositedbetween the sealing faces, making it difficult to keep the sealingfunction in a good shape for a long period. Also, the sealing faces willbe worn in contact with the polishing solution 106, losing sealingfunction in a short period. Another problem is that wear particles fromthe seal faces and ingredients dissolving out of the elastic seal willget mixed in polishing solution 106, hampering the polishing of wafersurface 109 a. The intrusion and deposition of such abrasive grains andthe wearing of the sealing faces occur more evidently in particular byswitching the slurry fluid feeding and discharging passages 105, 108from positive pressure to negative pressure or dry mode. Especially inthe dry mode, in addition, seizure will be inflicted on the sealingfaces because of frictional heat. If the intrusion and deposition ofabrasive grains and the wearing of the sealing faces affect the sealperformance, polishing solution 106 can leak out of the sealing faces,causing such problems as staining wafer surface 109 a and creeping intothe bearings between the first and second joint bodies and hindering thepolishing pad shaft 104 from rotating smoothly. And good polishing couldhardly be hoped for of such a rotary joint 101.

Those problems are encountered with the prior art rotary joint 101 notonly in the aforesaid surface polishing apparatus but in a rotaryequipment in which a slurry fluid like polishing solution or a corrosivefluid must flow between component parts rotating at a rate higher than acertain level. Such being the case, it has been keenly desired that asolution to the problems should be found, but the fact is that no rotaryjoint for fluids has been developed which exhibits a stabilized sealingperformance for a long time.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide arotary joint which permits smooth flow of a flurry fluid such as apolishing solution or a corrosive fluid through relatively rotatingcomponent parts without leakage and which makes a surface polishingapparatus or other equipment properly perform the functions as mentionedearlier.

It is another object of the present invention to provide a rotary jointthat always exhibits a good and stable sealing performance irrespectiveof the sealing conditions such as the pressure and properties of fluid,thus perfectly preventing the contamination of fluids and theenvironment and which is suitable for use in a variety of equipmentwhere a high degree of cleanness is required.

It is still another object of the present invention to provide a rotaryjoint which permits simultaneously smooth flow between the two jointbodies of a slurry fluid like polishing fluid and one or more kinds ofliquids or gases, thus opening up a wide range of applications.

It is yet another object of the present invention to provide a rotaryjoint that can be reduced in size to a maximum extent.

Those objects are attained by a rotary joint constructed according tothe present invention.

The rotary joint of the present invention comprises: a first joint body;a second joint body connected to the first joint body such that thesecond joint body is allowed to rotate in relation the first joint body;and a prime seal unit installed between opposed end portions of the twojoint bodies, the opposed end portions arranged in the direction of theaxis of rotation; and a continuous line of prime fluid passage whichruns through the two joint bodies. The prime seal unit is a mechanicalseal comprising: a stationary seal ring fixed concentrically on one ofthe opposed end portions of the two joint bodies with the axis ofrotation as its center; a movable seal ring held on the other of theopposed end portions, concentric with the stationary seal ring andmovable in the axial direction; a rotation stopper provided in the outercircumferential portion of the movable seal ring for preventing themovable seal ring from relative rotation while allowing the movable sealring to move in the axial direction; and a thrusting mechanism thaturges the movable seal ring against the stationary seal ring. And theseal unit is so built as to work as a seal between the outer and innercircumferential regions by the sliding contact between the relativelyrotating two ring seals. The prime fluid passage is formed out of theinner circumferential or inside region of the two seal rings, a firstprime fluid passage section which passes through the first joint bodyand opens at the inside region, and a second prime fluid passage sectionwhich passes through the second joint body and opens into the insideregion.

In a preferred embodiment, one of the two opposed end faces of the twoseal rings in the aforesaid seal unit is tapered or sharpened. In otherwords, one of the opposed seal end faces of the seal rings is in acircular form with a small width in the radial direction. The width inthe radial direction of the circular face is set at preferably 0.1 to0.8 mm, more preferably 0.4 to 0.7 mm. It is also desirable that theinner and outer circumferential faces forming the tapered or sharpenedseal are conical in sectional shape and are at an identical angle of 105to 150° C. relative to the seal end face.

It is also desired that the prime seal unit is formed as a mechanicalseal with 0≦K≦0.6 wherein K is the balance ratio.

The seal rings in the prime seal unit are made of silicon carbide,aluminum oxide, fluororesin or PEEK (polyether ether ketone). Itdesirable that at least the seal end faces of the seal rings should bemade of silicon carbide. Preferred grades of silicon carbide for thepurpose are not higher than 200 ppm in total metal content.

It is desirable that the stationary seal ring is made in a cylindricalform and fitted over the end of the joint body or fitted into a recessformed in the end portion of the joint body.

In case it is required that the prime fluids flowing in the main fluidpassage not be contaminated with metals in the rotary joint, it isdesired that the parts of the prime fluid passage which come intocontact with the fluids should be made of a material that does notrelease metal components when coming into contact therewith.

The material that does not release metal components when into contactwith the fluid means a material that does not give off metal ions whencoming into contact with the fluid flowing through the prime fluidpassage or which, in case the fluid contains solid ingredients such asabrasive grains, does not produce metal particles when coming intocontact with the solid ingredients. Among such materials are generallyplastics and silicon carbide. The ways of forming with such a materialthe parts of the fluid passage coming into contact with the fluidinclude the following two examples: one in which only the parts comingin direct contact with the fluid is made of those materials as bycoating; and the other case where the component parts of the two jointbodies in which fluid passages are formed, or all the component parts ofthe two joint bodies and the seal rings, are made of those materials. Itis desired that at least the inside walls of the respective prime fluidpassage sections (including the component parts of the two joint bodiesor the whole of the two joint bodies) are made of a plastic materialinert in or resistant to the flowing fluid, for example. The inert orresistant plastic material is selected on the basis of the properties ofthe fluid. If, for example, the fluid contains solid ingredients such asabrasive grains, a plastic material to be selected should be free fromwearing and releasing particles when coming into contact with the solidingredients. If the fluid is hot in temperature, the plastic material tobe selected should be thermo-resistant. If the fluid is corrosive, theplastic material to be selected should be resistant to corrosion.Concrete examples are engineering plastics such as PEEK, PES(polyethersulfone), and PC (polycarbonate) which are free from wearingand releasing particles when coming into contact with the solidingredients such as abrasive grains and excellent in work dimensionalstability and heat resistance and corrosion-resistant plastics such asPTFE (polytetrafluoroethylene plastic), PFA (tetrafluoroethyleneperfluoroalkoxy vinyl ether copolymer), and FEP (fluorinated ethylenepropylene copolymer plastics).

In a preferred embodiment, there is provided a cooling water space wherethe cooling water is supplied and circulated to cool the contact area ofthe two seal rings. This space is a region on the outer circumferentialside of the two seal rings, formed between the outer circumferentialsurface of the second joint body and the inner circumferential surfaceof the first joint body and sealed with a seal unit provided on thecircumferential surfaces and the prime seal unit. In this arrangement,it is desirable that the first joint body is provided with an inlet portand an outlet port which open into the cooling water space so that thecooling water may be circulated.

Furthermore, in case a fluid has to flow through a passage other thanthe prime fluid passage, a continuous line of auxiliary fluid passage isformed from two auxiliary fluid passage sections and a connectingregion. The connecting region is a space between the outercircumferential surface of the second joint body and the innercircumferential surface of the first joint body which concentricallyencircles the second joint body, and is sealed with a couple ofcircumferential side seal units placed therebetween and arranged in thedirection of axis of rotation. The first and second auxiliary fluidpassage sections open at the connecting region and are formed in such away as not to cross the prime fluid passage sections.

A preferred circumferential seal unit is a mechanical seal comprising astationary seal ring that is fixed to the inner circumferential surfaceof the first joint body and a rotary seal ring which is held on theouter circumferential surface of the second joint body—concentricallywith, and opposite to the stationary seal ring, movable in the axialdirection and urged against the stationary seal ring.

In such an arrangement, it is desirable that the inner circumferentialsurface of the stationary seal ring in at least one of thecircumferential side seal units serves as a ring-formed bearing fittedover the outer circumferential surface of the second joint body, whileallowing the second joint body to remain rotatable. In thecircumferential seal units, a plate spring elastically changeable inform in the axial direction is preferred as thrusting mechanism to urgethe rotary seal ring against the stationary seal ring. The seal rings inthe circumferential side seal unit is made of silicon carbide, aluminumoxide, fluororesin, PEEK, or carbon. It is desired that one of the twoseal rings in the circumferential side seal unit is made of siliconcarbide and the other made of carbon.

In the respective joint bodies, it is also desired that at least theinside wall of the auxiliary fluid passage sections is made of a plasticmaterial inert in or resistant to the fluid that flows through theauxiliary fluid passage sections. Depending on the properties of theflowing fluid, a plastic material is selected from among suchengineering plastics as PEEK, PES, and PC, and corrosion-resistantplastics such as PTFE, PFA, and FEP.

The contact areas between the seal rings in the prime seal unit and inthe circumferential side seal unit and the joint bodies are secondarilysealed by an O-ring. A preferred O-ring is made of fluororubber orfluororesin.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical, sectional view of an example of the rotary jointembodying the present invention.

FIG. 2 is an enlarged view of a core portion of FIG. 1.

FIG. 3 is an enlarged view of another core portion of FIG. 1.

FIG. 4 is a vertical, sectional view of a variation of the rotary jointembodying the present invention.

FIG. 5 is an enlarged view of a core portion of FIG. 4.

FIG. 6 is a vertical, sectional view corresponding to FIG. 1 showinganother variation of the rotary joint embodying the present invention.

FIG. 7 is an enlarged view of a core portion of FIG. 6.

FIG. 8 is a vertical, sectional view corresponding to FIG. 1 showingstill another variation of the rotary joint embodying the presentinvention.

FIG. 9 is an enlarged view of a core portion of FIG. 8.

FIG. 10 is a schematic side view of a surface polishing apparatusequipped with a rotary joint.

FIG. 11 is an enlarged view of a core portion of FIG. 10.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 to 9 show preferred embodiments of the rotary joint of thepresent invention. It is to be understood that the terms “upper” or“above” and “lower” or “below” are used for convenience' sake indescribing the present invention and applicable on those drawings only.

Embodiment 1

FIGS. 1 to 3 show a first embodiment of the present invention.

This embodiment concerns an example in which the present invention isapplied to the rotary joint 101 to be mounted on the surface polishingapparatus as described earlier. As shown in FIG. 10, the rotary joint101 is placed between the pad shaft support block 103 and the polishingpad shaft 104 so that the slurry fluid feeding and discharging passage105 on the non-rotary side may communicate with the slurry fluid feedingand discharging passage 108 on the rotary side.

The rotary joint of the present invention in this embodiment—the firstrotary joint 101A—, as shown in FIG. 1, comprises: a first joint body 1to be fixed to the pad shaft support block 103; a second joint body 2 tobe fixed to the polishing pad shaft 104; a prime seal unit 3 and aplurality of circumferential side seal units 4, 5 to be placed betweenthe two joints 1, 2; and a continuous line of prime fluid passage orslurry fluid passage 6; and an auxiliary fluid passage or non-slurryfluid passage 7.

The first joint body 1, as shown in FIG. 1, comprises a cylindrical sidewall 10 having an inner circumferential surface 10 a and an end wall 11fixed on the top of the side wall 10 to block the top. The side wall 10is made of a metal material such as stainless steel (in this example,the grade of steel having the JIS designation “SUS 304.” The end wall 11is made of engineering plastics such as PEEK, PES, and PC which are freefrom wearing and releasing particles when coming into contact withabrasive grains and excellent in work dimensional stability and heatresistance, because a first slurry fluid passage section 60 wherepolishing solution 106 flows is formed in the end wall 11, as will bedescribed later. In this example, PEEK is used.

The second joint body 2 is formed, as shown in FIG. 1, of a cylindricalmain part 20, a seal ring retainer 21 formed at the top of the main part20, a disk-like flange portion 22 formed at the bottom of the main part20, and a cylindrical sleeve 23 fitted over the main part 20. The partsof the second joint body 2 except for the sleeve 23—the main part 20,the seal ring retainer 21, and the flange portion 22—are integrallyformed. Those parts 20, 21, and 22 have a second slurry fluid passagesection 61 for polishing solution formed therein, as will be describedlater. Hence, as the first slurry fluid passage section 60, those partsare made of engineering plastics that are wear resistant to abrasivegrains and excellent in work dimensional stability and heat resistance,such as PEEK, PES, and PC. In the present example, PEEK is used. Sealring retainer 21 is concentric with main part 20 and circular in sectionwith a smaller diameter than that of the main part. Like side wall 10,sleeve 23 is made of a metal material such as stainless steel. In thepresent embodiment, the grade of stainless steel having the JISdesignation “SUS 304” is used.

Second joint body 2 is supported by the first joint body and isrotatable, with a bearing 13 placed between side wall 10 and sleeve 23at the lower ends thereof and with the parts of the second joint bodyexcept for the flange portion 22—the main part 20, the seal ringretainer 21, and the sleeve 23—inserted into the first joint body 1. Thesecond joint body 2, the flange portion 22 of which is mounted on thepolishing pad shaft 104, is forced to turn with the polishing pad shaft104, as is evident from FIGS. 1 and 10.

The prime seal unit 3 is made up, as shown in FIGS. 1 and 2, of astationary seal ring 30 provided on the second joint body 2, a movableseal ring 31 provided on the first joint body 1, a rotation stopper 32and a thrusting mechanism 33 provided between the movable seal ring 31and the first joint body 1.

The stationary seal ring 30 is made up, as shown in FIG. 2, of aring-formed main part 30 a and a cylindrical fixing part 30 b providedthereunder and integrally formed with the main part 30 a. Made ofsilicon carbide, the ring 30 is fixed concentrically to the second jointbody 2 with the fixing part 30 b fitted over the seal ring retainer 21.The upper end face of the main part 30 a is a smooth seal end face 30 cperpendicular to the axial direction of the second joint body 2. Thefitting area between the stationary part 30 b and the seal ring retainer21 is provided, for secondary sealing, with an O-ring 24 held in theouter circumferential portion of the seal ring retainer 21. The O-ring24 is made of fluororesin or fluororubber, for example, “Viton” orKalrez” (Du Pont).

The movable seal ring 31, made of silicon carbide, includes aring-formed main part 31 a and a cylindrical retainer 31 b provided atthe upper end thereof and integrally formed therewith, as shown in FIG.2. The ring 31 is held in the first joint body 1 concentrically with thestationary seal ring 30, and is movable in the axial direction, with theretainer 31 b fitted into a retention hole 11 a formed in the end wall11. The fitting area between the retainer 31 b and the retention hole 11a is provided, for secondary sealing, with an O-ring 14 held in theinner circumferential portion of the retention hole 11 a. The O-ring ismade of fluororesin or fluororubber such as, for example, “Viton” or“Kalrez” (Du Pont). The outside diameter of the main part 31 a isdesigned to be larger than that of the retainer 31 b by a certain size.The lower end portion of the movable seal ring 31 is pointed in verticalcross section, with the outer circumferential surface of the main part31 a tapering or diminishing in diameter toward the lower end while theinner circumferential surface expanding. The lower end face of thepointed lower end portion of the movable seal ring 31 is an annular sealend face 31 c which is concentric with and comes in linear contact withthe seal end face 30 c. The outside diameter of the seal end face 31 cis roughly equal to that of the retainer 31 b.

The rotation stopper mechanism 32 keeps the movable seal ring 31 fromrotating in relation to the first joint body 1 while allowing the ring31 to move in the axial direction. This mechanism 32 is provided, asshown in FIG. 2, in the lower end portion of the end wall 11 of thefirst joint body 1. One or a plurality of rotation stoppers 32 a areembedded in the axial direction in the outer circumferential portion ofthe retention hole 11 a. In the outer circumferential portion of themain part 31 a of the movable seal ring 31 is formed one or moreengaging holes 32 b with which the stopper pins 32 a engage.

The thrusting mechanism 33 comprises, as illustrated in FIG. 2, aplurality of springs 33 a placed between the upper end of the main part31 a of the movable seal ring 31 and the opposing lower end of the endwall 11 of the first joint body 1, thrusting the movable seal ring 31toward the stationary seal ring 30 so that the two seal end faces 30 c,31 c may be urged against and come into contact with each other.

The prime seal unit 3 works the same way as mechanical seals of theend-face contact type. In other words, with the second joint body 2rotating, the rotational sliding contact provides sealing between theseal end faces 30 c, 31 c, that is, between the region 3 a on the innercircumferential side of the two seal rings 30, 31 (the first connectingregion) and the region 3 b on the outer circumferential side of thesame. In this connection referring to FIGS. 2, 6 and 10, it is to benoted, it is desired that factors such as the dimensions of therespective components including the diameter of the pointed seal endface 31 c are set so as to ensure and maintain a good sealingperformance of the seal end faces 30 c, 31 c regardless of inversion ofthe pressure relationship between regions 3 a and 3 b occurring when thepolishing solution feeding and discharging mechanism 107 is under anegative pressure mode (as the slurry fluid passage 6 is switched to thedry mode). Those factors are preferably set, for instance, so as tobring the balance ratio to zero, which will be described later.

In addition, a plurality of circumferential side seal units are providedbetween the sleeve 23 or the outer circumferential portion of the secondjoint body 2 and the inner circumferential portion of the first jointbody 1, i.e. inner circumferential surface 10 a of the side wall 10which concentrically surrounds the sleeve 23. In the present example,first and second circumferential side seal units 4, 5 are installedbetween the sleeve 23 and the inner circumferential surface 10 a of theside wall 10 and arranged in the direction of rotation axis (verticaldirection) of the second joint body, as shown in FIG. 1.

The first circumferential side seal unit 4 is a mechanical seal of theend-face contact type placed between the side wall 10 and the sleeve 23as shown in FIGS. 1 and 3, which seals the lower end of the region 3 bat the outer circumference the seal rings 30, 31. And the region 3 bserves as cooling water space 3 b. To further illustrate, the firstcircumferential side seal unit 4 is formed, as illustrated in FIG. 3,of: a carbon stationary seal ring 43 fitted and held in the innercircumferential surface 10 a of the side wall 10 with an O-ring 42placed therebetween; a rotary seal ring 45 of silicon carbide held belowthe stationary seal ring 43 and around the sleeve 23 movable in theaxial direction with an O-ring 44 placed between the ring 45 and thesleeve 23; a spring retainer 46 fixed to the sleeve 23 below the rotaryseal ring 45; and a spring 47 put between the rotary seal ring 45 andthe spring retainer 46 to push the rotary seal ring 45 toward thestationary seal ring 43. And the relative rotation of and slidingcontact between the two seal rings 43 and 45 produces a seal between theouter circumferential region 4 a and the inner circumferential region,that is, the cooling water space 3 b. The rotary seal ring 45 is held inthe second joint body 2 and movable in the axial direction but notrelatively rotatable with an engaging protrusion 46 a engaging with anengaging groove 45 a as illustrated in FIG. 1. The protrusion 46 a isformed on the spring retainer 46 while the engaging groove 45 a isprovided in the outer circumferential portion of the rotary seal ring45. The spring 47 used in this example is a dish-like plate spring asshown in FIG. 3.

Thus, the cooling water 8 is fed into the cooling water space 3 bthrough an inlet port 10 b provided in the side wall 10 of the firstjoint body 1 as shown in FIGS. 1 and 2. It is designed that this coolingwater 8 cools the seal rings 30, 31 of the prime seal unit 3. Thecooling water used there is generally clean water at room temperature.The side wall 10 has an outlet port 10 c formed in the side wall 10which opens into the cooling water space 3 b so that the cooling water 8may circulate within the cooling water space 3 b.

The second circumferential side seal unit 5 is also a mechanical seal ofthe end-face contact type provided below the first circumferential sealunit 4 and between the side wall 10 and the sleeve 23. The second unit 5is of the same construction as, but axial symmetrical to, the first unit4. To further illustrate, the second circumferential side seal unit 5 isformed, as shown in FIG. 3, of the following components: a carbonstationary seal ring 53 fitted and fixed in the inner circumferentialsurface 10 a of the side wall 10 with an O-ring 52 placed therebetween;a rotary seal ring 55 of silicon carbide held above the stationary sealring 53 and around the sleeve 23 and movable in the axial direction withan O-ring 54 placed therebetween; the spring retainer 46 clamped on thesleeve 23 above the rotary seal ring 55; and a spring 57 put between therotary seal ring 55 and the spring retainer 46 to push the rotary sealring 55 toward the stationary seal ring 53. And the relative rotation ofand sliding contact action between the two seal rings 53 and 55 producesa seal between the outer circumferential region 4 a and the innercircumferential side atmospheric region 4 b on the bearing side. Thespring retainer 46 is shared with the first circumferential seal unit 4.Just as with the rotary seal ring 45 in the first circumferential sideseal unit 4, the rotary seal ring 55 is held in the second joint body 2and is movable in the axial direction but not relatively rotatable withan engaging protrusion 56 a engaging with an engaging groove 55 a. Theprotrusion 56 a is formed in the spring retainer 46, while the groove 55a is provided in the outer circumferential portion of the rotary sealring 55. The outer circumferential region 4 a is a connecting region 4a—referred to hereinafter as a second connecting region—with theloop-formed region between the outer and inner circumferential surfaces10 a, 23 closed at the upper and lower ends by the first and secondcircumferential side seal units 4, 5. The O-rings 42, 44, 52 and 54 areall made of fluororubber or fluororesin like the O-rings 14, 24.

The slurry fluid passage 6 is a continuous one formed out of the firstprime fluid passage section or the first slurry fluid passage section 60formed in the first joint body 1 and the second prime fluid passagesection or the second slurry fluid passage section 61 formed in thefirst joint body 2, the two sections 60, 61 communicating with eachother via the first connecting region 3 a which is sealed by the primeseal unit 3. The passage 6 is to be connected to the slurry fluidfeeding and discharging passages 105, 108. The first slurry fluidpassage section 60 is formed in the end wall 11 of the first joint body.One end of the first slurry fluid passage section 60 leads into thefirst connecting region 3 a and the other end opens in the outercircumferential surface of the end wall 11. To this opening is connectedthe slurry fluid feeding and discharging passage 105 on the non-rotaryside of the pad shaft support block 103 on which the first joint body 1is mounted. The second slurry fluid passage section 61 passes throughthe main part 20 of the second joint body 2, seal ring retainer 21 andflange portion 22 along the axis of rotation of the second joint body 2.One end of the second slurry fluid passage section 61 leads into thefirst connecting region 3 a with the other end opening at the lower endpart of the flange portion 22. This opening is to be connected to theslurry fluid feeding and discharging passage 108 on the rotary side orthe polishing pad shaft 104 on which the second joint body 2 is mounted.

To get the surface polishing work done better with the surface polishingapparatus, it is desirable that a pad head 104 a is provided with aplurality of air blasting ports 108 a around the opening of the slurryfluid feeding and discharging passage 108 on the rotary side, as shownin FIG. 11. Compressed air is blasted out through those air blastingports 108 a, so as to help disperse polishing solution 106 uniformly asthe solution 106 is jetted out to between the pad head 104 a and siliconwafer 109, and also to remove the polishing residue from between the twoparts 104 a, 109 as swiftly as possible.

The auxiliary fluid passage, that is, the non-slurry fluid passage 7 isformed to supply compressed air 106 a to those air blasting ports 108 a.As illustrated in FIGS. 1 and 3, the passage 7 is a continuous passageformed from a first auxiliary fluid passage section or a firstnon-slurry fluid passage section 70 formed in the first joint body 1 anda second auxiliary fluid passage section or a second non-slurry fluidpassage section 71 formed in the second joint body 2, the two sectionscommunicating with each other through the second connecting region 4 awhich is closed by the first and second circumferential seal units 4, 5.The first non-slurry fluid passage section 70 which leads into thesecond connecting region 4 a passes through the side wall 11 of thefirst joint body 1. To this first non-slurry fluid passage section 70 isconnected an air feeder 72 led to a suitable compressed air feedingsource (not shown) through which the non-slurry fluid, that is,compressed air 106 a is supplied. The secondary non-slurry fluid passagesection 71 includes a circular path 71 a formed by closing a tubularspace around the outer circumferential surface of the main part 20 withthe sleeve 23, a circular path 71 b or a ring-formed space surroundingthe second slurry passage section 61 and opening at the lower end of theflange portion 22, a path 71 c formed in the main part 20 to connect thetwo circular paths 71 a, 71 b, and an inlet path 71 d which is formed inthe sleeve 23 and the spring retainer 46 for allowing the circular path71 a to communicate with the second connecting region 4 a. The circularpath 71 b or the lower opening portion of the second non-slurry fluidpassage section 71 is so designed to communicate with the air blastingports 108 a when the second joint body 2 is attached to the polishingpad shaft 104.

In the surface polishing apparatus as shown in FIG. 10, the rotary jointthus constructed—the first rotary joint 101A—can feed and suck polishingsolution 106 without such problems as mentioned earlier and ensure thepolishing of the surface of silicon wafer 109 by the surface polishingapparatus with satisfactory results.

That is, in polishing operation with a rotating polishing pad shaft 104,the polishing solution 106 from the feeding and discharging mechanism107 flows through the slurry fluid feeding and discharging passage 105on the non-rotary side in the pad shaft support block 103 and the slurryfluid passage 6 in the rotary joint (the first rotary joint 101A) to theslurry fluid feeding and discharging passage 108 of the polishing padshaft 104 on the rotary side. In the slurry fluid passage 6, the firstslurry fluid passage section 60 in the first joint body 1 and the secondslurry fluid passage section 61 in the second joint body 2 are forced torotate in relation to each other as the polishing pad shaft 104 rotates.The polishing solution 106 flows through the slurry fluid passage 6without leaking from the two passage sections 60, 61, because the firstconnecting region 3 a connecting the two passages 60, 61 is sealed bysliding contact between the stationary seal ring 30 and the movable sealring 31 which rotate relative to one another.

There could be a concern that the polishing solution 10 may stick to andaccumulate at the contact area between the two seal rings 30, 31. But,in fact, any such stuck material would be scraped off by the pointed endof the movable seal ring 31. No solid ingredients or abrasive grains inthe polishing solution 106 are allowed to get into and deposit betweenthe two seal end faces 30 c, 31 c. That is, the two seal end faces 30 c,31 c are kept in a good contact condition, leaving no possibility thatthe seal will fail because of improper contact between the two seal endfaces 30 c, 31 c. Furthermore, the two seal end faces 30 c, 31 c willnot seize up, being cooled by the cooling water 8 supplied to thecooling water space 3 b.

It is also noted that the two seal rings 30, 31 are made of a super hardmaterial, silicon carbide, and will not wear and release particles inthe course of contact of seal end faces 30 c, 31 c. That is, there is noconcern that wear particles will get into the polishing solution 106,unlike the case with seal rings made of metal or carbon, or acombination of a seal ring made of such a super hard material as siliconcarbide and a seal ring formed from such a soft material as carbon, asin conventional mechanical seals of the end-face contact type.

The inner circumferential surface of the slurry fluid passage 6 isformed with a material which will not release particles such as wearparticles in contact with the polishing solution 106, especiallyabrasive grains. That is, the parts in the first joint body where thefirst slurry fluid passage section 60 is formed (the end wall 11) andthe parts in the second joint body where the second slurry fluid passagesection 61 is formed (the main part 20, seat ring retainer portion 21and flange portion 22) are formed with engineering plastics such asPEEK, PES, and PC. Those materials do not wear and release particles incontact with the abrasive grains, and are excellent in work dimensionalstability and thermal resistance. In the present example, PEEK is used.The connecting region (first connecting region 3 a) between the twoslurry fluid passage section 60, 61 is surrounded with the innercircumferential surfaces of the seal rings 30, 31 made of siliconcarbide which is wear resistant to abrasive grains. That precludes thepossibility of wear particles being given off from the passage wallsurface while the polishing solution 106 flows through the slurry fluidpassage 6.

The rotation stopper mechanism 32 and the thrusting mechanism 33 areindispensable components to ensure satisfactory seal performance byallowing the seal end faces 30 c, 31 c to rotate relative to one anotherunder a proper contact pressure. The component parts of stopper pins 32a and springs 33 a are made of a metallic material. If those componentparts were in the slurry fluid passage 6, metal particles would come offin contact with the abrasive grains and creep in the polishing solution106. But the two mechanisms 32, 33 are provided on the outercircumferential side of the movable seal ring 31, and there is nothingin the slurry fluid passage 6 that could contact the abrasive grains orhinder the flow of the polishing solution 106. Therefore, there is nopossibility that no metal particles will be released into the flow ofthe polishing solution in the slurry fluid passage 6.

Thus, polishing solution 106, when passing through slurry fluid passage6, is well sealed without wear particles getting mixed, and then isjetted out from the slurry fluid feeding and discharging passage 108 onthe rotary side to between the pad head 104 a and the silicon wafer 109to polish the wafer surface 109 a.

From pad head 104 a, compressed air 106 a is blasted out along with thepolishing solution, as indicated in FIG. 11. The air as blasted outhelps uniformly disperse the polishing solution 106 between pad head 104a and silicon wafer 109 and removes residues to further promote thepolishing of the wafer surface 109 a.

That is, the compressed air 106 a is fed from the air feeder 72 to theair blasting port 108 a through the non-slurry fluid passage 7 in thefirst rotary joint 101A. In the non-slurry fluid passage 7, the firstnon-slurry fluid passage section 70 in the first joint body 1 and thesecond non-slurry fluid passage section 71 in the second joint body 2are forced to rotate in relation to each other as the polishing padshaft 104 turns. Since the second connecting region 4 a which connectsthe two passage sections 70, 71 is sealed by the first and secondcircumferential side seal units 4, 5, the compressed air 106 a passesthrough the non-slurry fluid passage 7 to the air blasting ports 108 awithout leaking from between the non-slurry fluid passage sections 70,71.

In the non-slurry fluid passage 7, the component parts of thecircumferential side seal units 4, 5 including springs 47, 57 exist,unlike in the slurry fluid passage 6. Because the flowing fluid is anon-slurry fluid like air 106 a, however, there will be no particlesgenerated in contact with the component parts. Also, the non-slurryfluid passage sections 70, 71 have metallic parts formed therein—theside wall 10, spring retainer 46 and sleeve 23—unlike the slurry fluidpassage sections 60, 61. But the fluid that flows is not a slurry fluidlike the polishing solution 106 but air 106 a, there are no particlescoming off from those parts in contact with the fluid 106 a (air). Thefirst and second circumferential seal units 4, 5 are formed from acombination of carbon seal rings 43, 53 and silicon carbide seal rings45, 55 like conventional mechanical seals of the end face contact type.But since the fluid to be sealed by the circumferential side seal units4, 5 is air 106 a, there is no need to give such considerations to theconfiguration and material of the seal rings as in forming the primeseal unit 3. In the first rotary joint 101A, as set forth above, care istaken to ensure smooth flow of the slurry fluid polishing solution 106and the non-slurry fluid compressed air 106 a between the relativelyrotating bodies by properly selecting the configuration and materialsfor the constituent sections of the fluid passage 6,7 and the seal ringsof the seal units 3, 4, 5, according to the properties of the fluidsthat flow.

After the polishing operation is ended, the pressure inside the slurryfluid passage 7 is switched from the positive pressure mode to thenegative pressure mode (dry mode). Under the negative pressure, too, theseal rings 30, 31 of the prime seal unit 3 are cooled by the coolingwater 8 and there is no seizure of the seal end faces 30 c, 31 c.

Embodiment 2

FIGS. 4 and 5 show a second embodiment of the present invention. In thepresent embodiment, the present invention is applied to a rotary jointwith two relatively rotating bodies 1, 2 through which are passed theprime fluid 106, such as pure water, for treatment of semiconductorwafer and the auxiliary fluid 106 a, like compressed air, to be blastedout from the polishing pad shaft 104.

That is, the rotary joint in the present embodiment of the invention—thesecond rotary joint 101B—as shown in FIG. 4, comprises: a first jointbody 1 to be fixed on the stationary component; a second joint body 2 tobe fixed to the rotary component; a prime seal unit 3 and first andsecond circumferential side seal units 4, 5 placed between the two jointbodies 1, 2; and a prime fluid passage 6 and an auxiliary fluid passage7. The second rotary joint 101B is of the same construction as the firstrotary joint 101A except for some points which will be described.Therefore, the reference numerals designating corresponding parts inFIGS. 4 and 5 are the same as those in FIGS. 1 to 3, and no descriptionwill be given of those numerals.

The second rotary joint 101B is so designed that part of the upper firstcircumferential side seal unit 4 serves as a bearing for the secondjoint body 2. As shown in FIGS. 4 and 5, the inner circumferentialsurface of the stationary seal ring 43 serves as a ring-formed bearingface 48 which fits over and holds the upper part of the sleeve 23 of thesecond joint body 2 such that the sleeve 23 is allowed to relativelyrotate. That is, the second joint body 2 is rotatably held in the firstjoint body 1 by the upper and lower ends by means of a bearing 13 andthe bearing face 48 at the lower and upper ends thereof. That ensuresmore smooth rotation of the joint without axial vibration as comparedwith the joint held by the bearing 13 alone. It is noted that there isprovided a very thin, ring-formed gap 49 between the bearing face 48 andthe sleeve 23 of the second joint body 2. The idea is that the coolingwater 8 enters the gap 49 and forms a lubricating film, which furtherenhances the bearing function of the face 48. The inside diameter of thebearing face 48 is selected to be roughly identical with the outsidediameter of the sleeve 23 on condition that the bearing face 48 fitsover and holds the sleeve 23 such that the sleeve 23 is not displaceablein the radial direction (that is, without axial vibration) but isrelatively rotatable. To be specific, it is desirable to select theinside diameter of the bearing face 48 that gives a ring-formed gap some0.1 mm thick between the bearing face 48 and the sleeve 23.

In the second rotary joint 101B, it is also noted, the area in contactwith the fluid of the prime fluid passage 6 is formed from a materialwhich will not give off metallic components on contact with the primefluid 106 such as pure water. In other words, of the component parts ofthe first joint body 1 and the second joint body 2, the following partsare made of engineering plastics such as PEEK, PES, and PC which arefree from wearing when coming into contact with abrasive grains andexcellent in work dimensional stability and heat resistance. Those partsare the end wall 11 in the first joint body 1 where the first fluidpassage section 60 is formed and the main part 20 in the second jointbody 2 where the second fluid passage section 61 passes, including theseal ring retainer portion 21 and flange portion 22 which are integrallyformed therewith. The seal rings 30, 31 are all made of silicon carbide.No such consideration needs to be given to other component parts of therotary joint, which do not come into contact with the prime fluid106—that is, those parts other than the aforesaid parts 11, 20, 30, and31. These other component parts includes parts 10, 13, 14, 23, 24, 32 a,33 a, 42, 44, 45, 46, 47, 52, 53, 54, and 57. There is no need to takeinto consideration releasing of metallic components in designing thoseparts, and what material to use is decided on according to the serviceconditions of the rotary joint. For example, the side wall 10 in thefirst joint body 1 and the sleeve 23 in the second joint body 2 are madeof a metal material such as the stainless steel grade under the JISdesignation “SUS 304” while the stationary seal rings 43, 53 are madefrom carbon and the rotary seal rings 45, 55 are made of siliconcarbide. The O-rings are made of Viton, and the stopper pins 32 a andthe thrusting mechanisms 33, 47, 57 are made of a metal material such asthe stainless steel having the JIS designation “SUS 316.”

Like the first rotary joint 101A, the second rotary joint 101B allowsthe prime fluid 106 to flow through the prime fluid passage 6 withoutleaking through the connecting region between the prime fluid passagesections 60, 61 which is sealed by the sliding contact between thestationary seal ring 30 and the movable seal ring 31 which rotaterelative to one another. Then, since the movable seal ring 31 is pushedtoward the stationary seal ring 30 by the thrusting mechanism 33, thetwo seal end faces 30 c, 31 c are kept in a proper contact even if therelative position relationship changes because of vibration or the like.In addition, because the second joint body 2 is supported by the bearingface 48 of the stationary seal ring 43 and the bearing 13 both at theupper and lower ends, the axial vibration of the second joint body 2 iseffectively prevented. Therefore, there is no concern that the two sealend faces 30 c, 31 c will change in relative positional relationship inthe radial direction. That is, the two seal end faces 30 c, 31 c arekept in a proper contact, with a good seal performance exhibited.

It is also noted that the end wall 11 of the first joint body 1 and themain part 20 of the second joint body 2 in which the prime fluid passage6 is formed are made of an engineering plastic material such as PEEK andthe seal rings 30, 31 are made of silicon carbide. That is, thosematerials do not release metal ions and the like in contact with theprime fluid 106 at the fluid contact area in the prime fluid passage 6,and no metal components get into the prime fluid 106.

It might be feared that if the main part 20 of the second joint body 2is made of a plastic material such PEEK, the main part 20 would expandbecause of frictional heat generated by the seal rings 30, 31, therebypreventing the seal end faces 30 c, 31 c from coming in proper contacton account of high contact pressure. That would be especially the casewith the seal construction where the seal end faces 30 c, 31 c come intolinear contact. But the metallic sleeve 23 is fitted over the main part20. Hence, even if the main part 20 is made of a plastic material with alow thermal conductivity, the thermal expansion of the main part 20 isgreatly reduced because of heat radiation by the sleeve 23 made of ametallic material with a high heat conductivity. Furthermore, thepresent example is so designed that the sleeve 23 comes into contactwith the cooling water 8 and the auxiliary fluid 106 a such ascompressed air. And those fluids 8, 106 a can be expected to havecooling effect. Those heat radiation and cooling effects keep the mainpart 20 from undergo thermal expansion, and there is no such fear asmentioned above. Further, provision of the metal sleeve 23 helps tosecure a sufficient degree of mechanical strength for the second jointbody 2 as a whole even if the main part 20, which is one of the maincomponents of the second joint body, is made of a plastic material witha low mechanical strength.

It is further noted that the prime fluid passage 6 can be switched fromthe positive pressure mode to the negative pressure mode or dry mode asnecessary. In that dry mode, the seal rings 30, 31 of the prime sealunit 3 is cooled by the cooling water 3. Because of the heat radiationeffected by the metal sleeve 23 and the cooling effect through contactwith the cooling water 8 and the auxiliary fluid 106 a, there is noconcern that seal end faces 30 c, 31 c will seize up.

It is also noted that in the non-slurry passage 7, the first auxiliaryfluid passage section 70 in the first joint body 1 and the secondauxiliary fluid passage section 71 in the second joint body 2 are forcedto rotate in relation to each other. Since the second connecting region4 a between the two passage sections 70, 71 is sealed by the first andsecond circumferential side seal units 4, 5, the auxiliary fluid 106 ais allowed to pass through the auxiliary fluid passage 7 without leakingfrom a region between the auxiliary fluid passage sections 70, 71. Then,since the second joint body 2 is supported at the upper and lower endsby the bearing 13 and the bearing face 48 provided on the stationaryseal ring 43 of the first circumferential side seal unit 4, the secondjoint body 2 is free from axial vibration. That is, there is no changein the positional relationship in the radial direction of the seal rings43, 45 and 53, 55 in the first and second circumferential side sealunits 4, 5. Thus, a good seal is secured by the circumferential sideseal units 4, 5, with no fear of the auxiliary fluid leaking out of theauxiliary fluid passage 7. This arrangement eliminates the need toinstall many bearings to prevent axial vibration of the second jointbody 2, because the stationary seal ring 43 in the first circumferentialseal unit 4 serves as a bearing. The reduces the number of bearings 13to a minimum and thus permits size reduction of the second rotary joint101B—size in the direction of rotation axis. In addition, dish-formedplate springs which occupy less space than coil springs are used assprings 47, 57. That further reduces the size of the second rotary joint101B.

In the aforesaid embodiments, the first and second rotary joints 101Aand 101B are additionally provided with the auxiliary fluid passage 7and the first and second circumferential seal units 4, 5 to seal thespace between the relatively rotating components 70, 71 so that aplurality of fluids 106, 106 a may be allowed to flow simultaneously.Needless to say, such an arrangement is not needed with rotary jointsintended for exclusive use for the prime fluid 106 and also forselective or alternative use for the prime fluid 106 and other fluids.The third embodiment shown in FIGS. 6 and 7 is an example where thepresent invention is applied to a rotary joint for such uses.

Embodiment 3

The rotary joint according to a third embodiment of the presentinvention the third rotary joint 101C—includes, as shown in FIGS. 6 and7, first and second joint bodies 1, 2 connected with each other androtatable relative to one another, a prime seal unit 3 and acircumferential side seal unit 4 placed between the two joint bodies 1,2 and a continuous line of prime fluid passage 6 formed in the two jointbodies 1, 2. The third rotary joint 101C is of the same construction asthe first rotary joint 101A or the second rotary joint 101B except forsome points which will be described. Therefore, the reference numeralsdesignating corresponding parts in FIGS. 6 and 7 are the same as thosein FIGS. 1 to 5, and no description will be given of those numerals.

The first joint body 1 is made up, as shown in FIG. 6, of a side wall 10formed from a first cylindrical body 10 d and a second cylindrical body10 e linked to the lower end thereof and an end wall 11 attached on thetop of the first cylindrical body 10 d and closing the opening thereof.

As illustrated in FIG. 6, the second joint body 2 looks like avertically extending cylinder, and rotatably linked to the first jointbody 1 via bearings 13 placed between the portion near the lower end ofthe second joint body 2 and the second cylindrical body 10 e of thefirst joint body 1. That is, the two joint bodies 1, 2 are linked toeach other such that the two joint bodies 1,2 are relatively rotatable,with the axis of the second joint body 2 as relative rotation axis. Atthe end of the second joint body 2, a threaded edge 27, over which thepolishing pad shaft is to be screwed, is formed, and an O-ring 28 totighten up the screwing is installed.

The prime seal unit 3 is a mechanical seal of the end face contact typeof the same construction as the first rotary joint 101A as shown inFIGS. 6 and 7. The unit 3 comprises a stationary seal ring 30 made ofsilicon carbide and provided in the second joint body 2, a movable sealring 31 made of silicon carbide and provided in the first joint body 1and a coil spring 33 a placed between the movable seal ring 31 and thefirst joint body 1. This unit 3 serves as seal between the innercircumferential region of the two seal rings 30, 31—the first connectingregion 3 a—and the outer circumferential region—the cooling water space3 b. To further make sure that there will be no metallic contaminationof prime fluids like polishing solution 106 for treatment of siliconwafer, the following features are incorporated.

First, different materials are selected properly for different parts ofthe rotary joint. The selection of materials is based on this. That is,the parts making up the mechanical seal, i.e. the prime seal unit 3, canbe classified according to the performance, strength, and otherproperties required as follows:

(1) Parts that can be made of a ceramic or plastic material so as not torelease metallic particles,

(2) Parts made of metallic materials including alloys that can be coatedwith a ceramic or plastic material on the surface to contain metallicparticles,

(3) Parts that cannot be made of or coated with a ceramic or plasticmaterial such that generation of metallic particles cannot be avoided,and

(4) Parts such as O-rings made of elastic materials that due to theirnature do not give rise to metallic particles.

With the parts under (1) and (2) such as the seal rings 30, 31 at leastthe areas which come into contact with the polishing solution 106 aremade of materials that do not release metal particles. The parts under(3), such as coil springs 33 a, are placed in the cooling water space 3b which does not come into contact with the polishing solution 106. Thatway, the possibility of metallic particles mixing into the polishingsolution 106 is precluded.

To be specific, of the parts under (1) and (2), the seal rings 30, 31are made of sintered silicon carbide. The end wall 11 of the first jointbody 1 and the second joint body 2 where the main fluid passage sections60, 61 are formed are made of engineering plastics such as PEEK, PES,and PC, which are excellent in work dimensional stability and heatresistance. Alternatively, they may be coated with a suitable plasticmaterial such as PTFE on the fluid contact area. That way, those partsare not capable of releasing metallic particles on contact with thepolishing solution 106 itself or its solid ingredients includingabrasive grains. The O-rings which come under (4) are made of an elasticmaterial such as fluroresin and fluororubber and naturally do notrelease metallic particles. The coil springs 33 a and stopper pins 32 awhich come under (3) are made of a metallic material. But as pointed outabove, those parts are placed in the cooling water space 3 b, which isoutside of the prime fluid passage 6, and they are not exposed to thepolishing solution 106. That is, those parts cannot cause the polishingsolution 106 to be contaminated with metallic particles. Unlike the coilsprings 33 a, the stopper pins 32 a in the rotation stopper mechanism 32can be treated the same way as the parts under (1) and (2). That way,those parts 32 a could be placed in the area where they are exposed tothe polishing solution 106.

Meanwhile, the seal end face 31 c of the movable seal ring 31 has afunction of scraping off and removing the abrasive grains that intrudebetween the seal end faces 30 c, 31 c. This function of removing stucksolid ingredients is achieved at a narrow width W in the radialdirection of the annular seal end face 31 c of the movable seal ring 31.It is also possible to prevent contact wearing at seal end faces 30 c,31 c by minimizing the width W of the seal end face 31 c, thus reducingthe contact area between the seal end faces 30 c, 31 c.

Secondly, therefore, the radial width W of the seal end face 31 c of themovable seal ring is set at 0.1 to 0.8 mm to effectively achieve thefunction of removing solid ingredients and the function of preventingthe contact wearing. If W>0.8 mm, the seal end face 31 c of the movableseal ring 31 can not work well to remove the solid ingredients andcannot effectively prevent the contact wearing of the seal end faces 30c, 31 c. If W<0.1 mm, on the other hand, there will arise such problemsas poor strength of the seal end face 31 c of the movable seal ring 31and excessive scraping by the seal end face 31 c. Excessive scrapingcould destroy the lubrication film or a fluid film of the polishingsolution 106 formed between the seal end faces 30 c, 31 c, with theresult that the contact areas of the seal end faces 30 c, 31 c seize up.Furthermore, the contact pressure between the seal end faces 30 c, 31 ccould rise more than necessary. That is, the contact wearing of the sealend faces 30 c, 31 c could not be suppressed effectively, resulting inreleased particles. The desired upper and lower limits of the seal endface width W are different depending on the seal conditions such as theproperties, pressure and other parameters of the prime fluid 106 to besealed. But it is preferable to set at 0.4 mm≦W≦0.7 mm irrespective ofthose seal conditions if the function of removing the solid ingredientsand preventing the contact wearing is to be ensured with the lubricationfilm well protected. The inclination angles α, β of the inner and outercircumferential surfaces of the tapering portion forming the seal endface of the movable seal ring 31—the lower end of the movable seal ring31—are set at 105 to 150 degrees in consideration of such factors as thestrength of the tapering portion forming the seal end face. For easymachining of the movable seal ring 31 and in consideration of otherfactors, it is so set that α=β, that is, 105°≦α=β≦150°.

In the meantime, the seal rings 30, 31 are made of sintered siliconcarbide that is free from releasing metallic particles in contact withthe polishing solution 106. But it would be possible that there wouldarise wear particles from the contact area of the seal rings 30, 31 inlong service. Silicon carbide which is generally used as material forthe seal rings 30, 31 contains heavy metals such as iron in considerablequantities. That is, the wear particles arising from the seal rings 30,31 could contain those metallic components. If those metallic componentsget into and contaminate the polishing solution 106, an adverse effectwill be produced on the silicon wafer.

Thirdly, in the third rotary joint 101C, therefore, that possibility isprecluded by forming at least the seal end faces 30 c, 31 c of the sealrings 30, 31 with silicon carbide having a low metal content (referredto hereinafter as low metal content silicon carbide) whose totalcontents of metals like iron are not higher than 200 ppm. That way,possible metallic contamination of the polishing solution 106 iseffectively prevented. In other words, if at least the seal end faces 30c, 31 c of the seal rings 30, 31 are made from such a low metal contentsilicon carbide, the metal contents in the wear particles generated bycontact between the seal rings 30, 31 can be reduced to a minimum.Coupled with the setting of the radial width W at 0.1 to 0.8 mm,preferably 0.4 to 0.7 mm, for suppressing as much as possible therelease of wear particles generated by contact between the seal rings30, 31, the use of the low metal content silicon carbide can reduce themetallic contamination of the polishing solution 106 to the extent thatthe wear particles arising from the contact area between the seal rings30, 31 will have no adverse effect on the silicon wafer. To ensure that,the whole seal rings 30, 31 are made of a low content grade of siliconcarbide. Or the seal end faces 30 c, 31 c alone are made of, that is,coated with, that material. In the present example, the whole seal rings30, 31 are made of a low metal content grade of silicon carbide.

The surface polishing apparatus as illustrated in FIG. 10 is oftenswitched from the positive pressure mode for polishing operation to thenegative pressure or dry mode to keep the residual polishing solutionfrom dropping on the finished wafer surface. In the mode switchover, thepressure within the prime fluid passage 6 changes with a negativepressure acting on the movable seal ring 31. With the negative pressureacting, the movable seal ring 31 would be moved away from the stationaryseal ring 30, such that the contact face pressure between the seal endfaces 30 c, 31 c is not maintained properly. That could result in thesucked residual polishing solution leaking out from between the seal endfaces 30 c, 31 c.

Fourthly, therefore, it is so designed that 0≦K≦0.6 is achieved, whereK=the balance ratio of the prime seal unit 3 so that the contact facepressure between the seal end faces 30 c, 31 c is maintained at adesired level even if such a negative pressure acts. To be morespecific, the outside diameter d₀ of the retainer portion 31 b of themovable seal ring 31, and the inside and outside diameters d₁ and d₂ ofthe seal end face 31 c are so set that 0≦K≦0.6 is achieved, with(d₂−d₁)/2(=w) being 0.1 to 0.8 mm, preferably 0.4 to 0.7 mm so that theseal end faces 30 c, 31 c are kept in proper contact with each otherregardless of changes in pressure and other conditions as, for instance,when the prime fluid passage 6 is switched from the blasting operationto the negative pressure mode for suction.

The balance ratio K can be specified by the diameters of the relativelyrotating and sliding contact area between the two seal rings 30, 31,that is, the inside and outside diameter d₁, d₂ of the seal end face 31c, and the diameter of the back pressure acting area of the movable sealring 31 movable in the axial direction, that is, the outside diameter doof the retainer portion 31 b of the movable seal ring 31. For designpurposes, the ratio K can be given as follows:K=(d₀)²−(d₁)²)/((d₂)²)−(d₁)²).

That is, the apparent face pressure (thrust) Pa acting on the slidingcontact areas of the two seal rings 30, 31 is produced by the fluidpressure (back pressure) P acting on the movable seal ring 31 to thrustthe same toward the stationary seal ring 30 and the pressure (springpressure) F of the thrusting mechanism 32. The apparent face pressure(thrust) Pa is given in the following equation:Pa=(π/4)((d₀)²−(d₁)²)P/(π/4)((d₂)²−(d₁)²)+(π/4)((d₂)²−(d₁)²)F/π/4)((d₂)²−(d₁)²)=((d₂)²−(d₀)²⁾/((d₂)²−(d₁)²))P+F.In this equation, the coefficient “((d₀)²−(d₁)²)/((d₂)²−(d₁)²)” is thebalance ratio K.

Therefore, the balance ratio K, which is ((d₀)²−(d₁)²)/((d₂)²−(d₁)²), isinevitably determined by the inside and outside diameter d₁, d₂ of theseal end face 31 c and the outside diameter d₀ of the retainer portion31 b. By designing d₀, d₁, d₂ so that 0≦K≦0.6 is achieved, it ispossible to keep the contact pressure of the two seal rings 30, 31 at aproper level to produce a good seal effect without much changes takingplace in the thrust Pa at the relatively rotating and sliding contactarea of the seal end faces 30 c, 31 c irrespective of the pressure inthe prime fluid passage 6. Otherwise, problems would arise. If K<0, thespring pressure F would have to be set higher than necessary, forexample. If K>0.6, then the contact pressure between the two seal rings30, 31 would be insufficient and the polishing solution 106 could leakout of the prime fluid passage 6 in discharging the residual polishingsolution, that is, in the negative pressure or dry mode. With 0≦K≦0.6,however, the polishing solution 106 can be sealed effectively regardlessof the pressure within the prime fluid passage 6, that is, whether thepassage 6 is under the negative pressure with a negative pressureacting.

The four features just described are applicable to the first and secondrotary joints 101A and 101B.

It is noted that in the third rotary joint 101C, such a mechanical sealas used in the first and second rotary joints 101A, 101B is not used ascircumferential side seal unit 4. The seal unit 4 used in this rotaryjoint 101C is made up, as shown in FIG. 6, of: a seal ring 49 a of anelastic material such as rubber which is fitted into, and held in, theinner circumferential surface of the first cylinder body 10 d, andpressed against the outer circumferential surface of the second jointbody 2; a reinforcing metal piece 49 b embedded in the sealing ring 49a; and a garter spring 49 c to secure a required strength with which theinner radial portion of the seal ring is pressed against the secondjoint body 2.

Embodiment 4

FIG. 8 and FIG. 9 show a fourth embodiment of the present invention. Therotary joint in this embodiment—the fourth rotary joint 101D—isidentical in construction with the first, second and third rotary joints101A, 101B, 101C except for some points which will be described.Therefore, the reference numerals designating corresponding parts inFIGS. 8 and 9 are the same as those in FIGS. 1 to 7, and no descriptionwill be given of those numerals.

In the fourth rotary joint 101D, the stationary seal ring 30 is formedin the shape of a cylinder as shown in FIGS. 8 and 9. Concentric withthe second joint body 2 with its axis of rotation as center, thestationary seal ring 30 is fitted into, and held in, a recess formed inthe seal ring retainer portion 21. On the top of the stationary sealring 30 is formed the seal end face 30 c, an annular smooth surfaceperpendicular to the axis. The stationary seal ring 30 is fitted intothe recess 21 a with the top end portion slightly protruding out andwith an O-ring 24 a placed in the fitted portion as secondary seal. Likethe O-ring 14, the O-ring 24 a is made preferably of fluororesin orfluororubber.

Since the stationary seal ring 30 must be closely fitted into the secondjoint body 2 unlike the rotary seal rings 45, 55 in the circumferentialside seal units 4, 5, machining with low precision or shrinkage fittingtechnique could result in residual strain, shrinkage fitting strain orthe like which could affect the seal function. The rotary joint 101C hasno problem of that kind, since the stationary seal ring 30 iscylindrical in shape with a major portion fitted into the recess 21 a ofthe second joint body 2.

The movable seal ring 31 is composed, as shown in FIGS. 8 and 9, of aring-formed main part 31 a and a cylindrical retainer portion 31 bintegrally formed therewith. Fitted into a retention hole 11 a providedin the end wall 11, the movable seal ring 31 is held in the first jointbody concentrically opposed to the stationary seal ring 30 and movablein the axial direction. The fitting area between the retainer portion 31b and the retention hole 11 a is secondarily sealed with an O-ring 14.The outside diameter of the main part 31 a is larger than the outsidediameter of the retainer portion 31 b by a specific size. The lower endface of the main part 31 a is the seal end face 31 c, an annular smoothsurface perpendicular to the axis. It is noted that the factors such asthe dimensions of the respective component parts including the diametersof the seal end faces 30 a, 31 c are selected so that a proper sealfunction may be maintained by the seal end faces 30 a, 31 c even whenthe pressure relation between the regions 3 a, 3 b is reversed, forinstance, when the first fluid passage 6 is switched to the negativepressure or dry mode. That is, the balance ratio K is so set that0≦K≦0.6 is achieved. It is also noted that the stationary seal ring 43in the first circumferential seal unit 4 has a bearing face 48 thatserves as a bearing for the second joint body 2 as in the second rotaryjoint 101B.

It is understood that the present invention is not limited to theembodiments just described but may be changed or modified withoutdeparting from the basic principle of the present invention.

For example, the rotary joints of the present invention can be soconfigured that three or more kinds of fluids can simultaneously flowthrough their respective passages. While it is structurally impossibleto build more than one prime fluid passage 6, the number of auxiliaryfluid passages 7 can be freely increased by providing additionalcircumferential side seal units 4, 5. In that case, it is desirable tohave one circumferential side seal unit serve as a seal between twosecond connecting regions 4 a, to diminish the size of the rotary joint101. This feature is adopted in the embodiments described above. Thatis, the first circumferential side seal unit 4 is used as seal for thecooling water space 3 b and the second connecting region 4 a. In case Nlines of auxiliary fluid passages 7 are needed to have (N+1) kinds offluids including the main fluid flow, N spaces of second connectingregions 4 a are needed. Those N spaces can be formed by providing (N+1)pieces of circumferential side seal units side by side.

While it is desirable to provide a bearing face 48 in the stationaryseal ring remotest from the bearing 13 (in the foregoing examples, thestationary seal ring 43 of the first circumferential seal unit 4), it ispossible to form the bearing face 48 c in another seal ring or aplurality of seal rings as well (in the above example, the stationaryseal ring 53 of the seal unit 5).

In the prime seal unit 3, needless to say, the stationary seal ring 30can be provided in the first joint body 1 and the movable seal ring 31(and its auxiliary parts 32, 33) in the second joint body 2—unlike thearrangement in the foregoing examples.

The rotary joints of the present invention are also possible to apply tosurface polishing apparatuses other than that illustrated in FIG. 10. Anexample is an apparatus so constructed that the rotary table is apolishing pad to blast polishing solution and the surface of siliconwafer is brought into contact with that pad table. The rotary joints ofthe present invention can also be used for a variety of equipment fortreating and handling other slurry fluids, corrosive fluids or the likethan the polishing solution 106. The rotary joints of the presentinvention are especially suitable for slurry fluids containing solidingredients like abrasive grains.

Depending on the properties and other conditions of the auxiliary fluid106 a to be sealed, a non-contact type mechanical seal—a gas seal—may beused as circumferential side seal unit to seal one or more secondconnecting regions 4 a.

The fluid contact area in the prime fluid passage 6 is made of amaterial that does not release metallic components such as metal ions incase the prime fluid 106 is pure water, polishing solution or the likefor treatment of silicon wafer. Such materials include engineeringplastics, corrosion-resistant plastics and silicon carbide. Asmentioned, the portion where the prime fluid passage 6 is formed alonemay be made of those materials. Or the fluid contact area alone may bebuilt of such materials as by coating. Or the whole joint bodies 1, 2 orthe whole rotary joint may be made of those materials. In case the wholejoint or the major part thereof is made of a plastic material, it isdesirable to select materials whose mechanical properties, especiallybending strength, are higher than a specific level. Generally, it isdesirable to use materials such as PEEK and PES with a bending strengthof not lower than 1,000 kg/cm².

The present invention is suitable for apparatuses and equipment handlingprime fluids 106 such as slurry fluid containing hard solid ingredientslike abrasive grains and corrosive liquids. Especially, in the case of ahighly corrosive prime fluid 106, the fluid contact area like the innerwall surface of the passage sections 60, 61 of the prime fluid passage 6may be coated with such corrosion-resistant plastics as PTFE, PFA andFER It is desirable to make the seal rings 30, 31 of silicon carbide.Those seal rings 30, 31 also may be formed with such engineering plasticmaterials.

The seal rings of the prime seal unit 3 and the seal rings of therespective circumferential side seal units 4,5 also may be made of lowmetal content silicon carbide of a total metal content of not higherthan 200 ppm. Those seal rings also may be built with common sinteredsilicon carbide with the seal end faces alone made with a low metalcontent grade of silicon carbide as by coating with a chemical vapordeposition layer of silicon carbide of such a grade.

The material for the seal rings 30, 31 in the prime seal unit 3 may beselected among aluminum oxide, fluororesin and PEEK in addition tosilicon carbide depending on the sealing conditions. The seal rings 30,31 are made of the same material or different materials. The materialfor the stationary seal rings 43, 53 and the rotary seal rings 45, 55 inthe circumferential side seal units 4, 5 may be selected from amongsilicon carbide, aluminum oxide, fluororesin, PEEK, and carbon. Of them,one material or a combination of two or more materials may be used, aswell as the aforesaid combination of carbon and silicon carbide. It isalso noted that in case silicon carbide is picked up as material forseal rings, it is possible to use commonly used sintered materialsdepending on the sealing conditions in addition to the aforesaid lowmetal content silicon carbide. The suitable crystal structure may beeither of the following: α type polycrystal, β type polycrystal or amixture of those two types. But it is desirable to have a vapordeposition coated layer of the β type silicon carbide polycrystal on theend face of the aforesaid sintered body.

The fluororubber to form O-rings 12, 24 etc. can be selected from amongvinylidene fluorides, acrylate fluorides, propylene hexafluorides, andtheir copolymers.

What is claimed is:
 1. A rotary joint comprising: a first joint body; asecond joint body rotatably connected to the first joint body; a primeseal unit which is a mechanical seal placed between opposed end portionsarranged in the axial direction of the two joint bodies, the prime sealunit comprising (1) a stationary seal ring fixed concentrically to oneof the opposed end portions with the axis of rotation as center, (2) amovable seal ring movable in the axial direction and held in the otherof the opposed end portions concentrically with the stationary sealring, (3) a rotation stopper mechanism provided on the outercircumferential side of the movable seal ring to keep the movable sealring from relatively rotating while allowing the movable seal ring tomove in the axial direction, and (4) a thrusting mechanism to press themovable seal ring toward the stationary seal ring, thereby providing aseal between an inner circumferential region inside the seal rings andan outer circumferential region outside of the seal rings by the slidingcontact of the two relatively rotating seal rings, wherein one of thetwo seal rings has a lower end portion that is tapered and sharpened;and a continuous line of prime fluid passage made up of the innercircumferential region within the two seal rings, a first prime fluidpassage section passing through the first joint body and leading intosaid inner circumferential region and a second prime fluid passagepassing through the second joint body and leading into said innercircumferential region.
 2. The rotary joint as defined in claim 1,wherein one of the opposed seal end faces of the two seal rings in theprime seal unit is an annular face 0.1 to 0.8 mm in width in the radialdirection.
 3. The rotary joint as defined in claim 1 or claim 3, whereinthe inner and outer circumferential surfaces of the tapered portion ofthe seal ring form circular cone surfaces which are at an identicalangle of 105 to 150 degrees with respect the seal end face.
 4. Therotary joint as defined in claim 1, wherein the prime seal unit is amechanical seal so built that 0≦K≦0.6 is achieved, where K is thebalance ratio.
 5. The rotary joint as defined in claim 1, wherein therespective seal rings in the prime seal unit are made of materialsselected from among silicon carbide, aluminum oxide, fluororesin, andPEEK.
 6. The rotary joint as defined in claim 5, wherein at least theseal end face of each seal ring is formed with silicon carbide.
 7. Therotary joint as defined in claim 5 or claim 6, wherein said siliconcarbide contains a total metal content of not higher than 200 ppm. 8.The rotary joint as defined in claim 1, wherein the stationary seal ringis cylindrical in shape and fitted and capped over one end portion ofthe joint body.
 9. The rotary joint as defined in claim 1, wherein thestationary seal ring is cylindrical in shape and fitted and held into arecess formed in one end portion of the joint body.
 10. The rotary jointas defined in claim 1, wherein the prime fluid passage is for liquid topass through, and wherein the fluid contact area in said prime fluidpassage is made of a material that will not release metal components incontact with the liquid.
 11. The rotary joint as defined in claim 1,wherein a circumferential side seal unit is provided between the outercircumferential surface of the second joint body and the innercircumferential surface of the first joint body surrounding said secondjoint body concentrically, whereby the outer circumferential regionoutside of said prime seal rings is sealed by said circumferential sideseal unit and said prime seal unit and is used as cooling water space tosupply cooling water to cool the contact area of the seal rings.
 12. Therotary joint as defined in claim 11, wherein the second joint body isprovided with an inlet port and an outlet port, both opening into saidcooling water space, so as to supply and circulate the cooling water.13. The rotary joint as defined in claim 1, wherein a plurality ofcircumferential seal units are provided side by side in the axialdirection between the outer circumferential surface of the second jointbody and the inner circumferential surface of the first joint bodysurrounding said second joint body concentrically, thereby forming aconnecting region sealed with the neighboring circumferential side sealunits between said outer and inner circumferential surfaces of saidjoint bodies, and wherein there are provided first and second auxiliaryfluid passage sections in the joint bodies which do not cross said primefluid passage sections, thereby forming a continuous line of auxiliaryfluid passage made up of the two auxiliary fluid passage sections andsaid connecting region.
 14. The rotary joint as defined in claim 11 orclaim 13, wherein the circumferential seal unit is a mechanical sealcomprising a stationary seal ring fixed to the inner circumferentialsurface of the first joint body and a rotary seal ring movable in theaxial direction, held in the outer circumferential surface of the secondjoint body concentrically with the stationary seal ring and pressedagainst the stationary seal ring.
 15. The rotary joint as defined inclaim 11 or claim 13, wherein the inner circumferential surface of thestationary seal ring in at least one circumferential side seal unitserves as a ring-formed bearing face which fits over and rotatably holdsthe outer circumferential surface of the second joint body.
 16. Therotary joint as defined in claim 11 or claim 13, wherein thecircumferential seal unit is provided with a plate spring elasticallychangeable in form in the axial direction for urging the rotary sealspring against the stationary seal spring.
 17. The rotary joint asdefined in claim 4, wherein the respective seal rings in thecircumferential seal units are made of materials selected from amongsilicon carbide, aluminum oxide, fluororesin, PEEK, and carbon.
 18. Therotary joint as defined in claim 17, wherein, of the two seal rings insaid circumferential seal units, one is made of silicon carbide and theother is made of carbon.
 19. The rotary joint as defined in claim 13,wherein at least the inner walls of the auxiliary fluid passage sectionsin the respective joint bodies are formed with a plastic material inertin and resistant to the auxiliary fluid that flows through saidauxiliary fluid passage sections.
 20. The rotary joint as defined inclaim 1, claim 11, or claim 13, wherein the O-ring secondarily sealingthe contact area between the seal ring and the joint body is made offluororubber or fluororesin.
 21. A rotary joint comprising: a firstjoint body; a second joint body rotatably connected to the first jointbody; a prime seal unit which is a mechanical seal placed betweenopposed end portions arranged in the axial direction of the two jointbodies, the prime seal unit comprising (1) a stationary seal ring fixedconcentrically to one of the opposed end portions with the axis ofrotation as center, (2) a movable seal ring movable in the axialdirection and held in the other of the opposed end portionsconcentrically with the stationary seal ring, (3) a rotation stoppermechanism provided on the outer circumferential side of the movable sealring to keep the movable seal ring from relatively rotating whileallowing the movable seal ring to move in the axial direction, and (4) athrusting mechanism to press the movable seal ring toward the stationaryseal ring, thereby providing a seal between an inner circumferentialregion inside the seal rings and an outer circumferential region outsideof the seal rings by the sliding contact of the two relatively rotatingseal rings, wherein the seal rings in the prime seal unit are made ofsilicon carbide with a total metal content of not higher than 200 ppm;and a continuous line of prime fluid passage made up of the innercircumferential region within the two seal rings, a first prime fluidpassage section passing through the first joint body and leading intosaid inner circumferential region and a second prime fluid passagepassing through the second joint body and leading into said innercircumferential region.
 22. A rotary joint comprising: a first jointbody; a second joint body rotatably connected to the first joint body; aprime seal unit which is a mechanical seal placed between opposed endportions arranged in the axial direction of the two joint bodies, theprime seal unit comprising (1) a stationary seal ring fixedconcentrically to one of the opposed end portions with the axis ofrotation as center, (2) a movable seal ring movable in the axialdirection and held in the other of the opposed end portionsconcentrically with the stationary seal ring, (3) a rotation stoppermechanism provided on the outer circumferential side of the movable sealring to keep the movable seal ring from relatively rotating whileallowing the movable seal ring to move in the axial direction, and (4) athrusting mechanism to press the movable seal ring toward the stationaryseal ring, thereby providing a seal between an inner circumferentialregion inside the seal rings and an outer circumferential region outsideof the seal rings by the sliding contact of the two relatively rotatingseal rings; and a continuous line of prime fluid passage made up of theinner circumferential region within the two seal rings, a first primefluid passage section passing through the first joint body and leadinginto said inner circumferential region and a second prime fluid passagepassing through the second joint body and leading into said innercircumferential region, wherein the prime fluid passage is for liquid topass through, and wherein the fluid contact area in said prime fluidpassage is made of a material that will not release metal components incontact with the liquid.
 23. A rotary joint comprising: a first jointbody; a second joint body rotatably connected to the first joint body; aprime seal unit which is a mechanical seal placed between opposed endportions arranged in the axial direction of the two joint bodies, theprime seal unit comprising (1) a stationary seal ring fixedconcentrically to one of the opposed end portions with the axis ofrotation as center, (2) a movable seal ring movable in the axialdirection and held in the other of the opposed end portionsconcentrically with the stationary seal ring, (3) a rotation stoppermechanism provided on the outer circumferential side of the movable sealring to keep the movable seal ring from relatively rotating whileallowing the movable seal ring to move in the axial direction, and (4) athrusting mechanism to press the movable seal ring toward the stationaryseal ring, thereby providing a seal between an inner circumferentialregion inside the seal rings and an outer circumferential region outsideof the seal rings by the sliding contact of the two relatively rotatingseal rings; a continuous line of prime fluid passage made up of theinner circumferential region within the two seal rings, a first primefluid passage section passing through the first joint body and leadinginto said inner circumferential region and a second prime fluid passagepassing through the second joint body and leading into said innercircumferential region; and a plurality of circumferential seal unitsprovided side by side in the axial direction between the outercircumferential surface of the second joint body and the innercircumferential surface of the first joint body surrounding said secondjoint body concentrically, thereby forming a connecting region sealedwith the neighboring circumferential side seal units between said outerand inner circumferential surfaces of said joint bodies, and whereinthere are provided first and second auxiliary fluid passage sections inthe joint bodies which do not cross said prime fluid passage sections,thereby forming a continuous line of auxiliary fluid passage made up ofthe two auxiliary fluid passage sections and said connecting region.